High-strength nanocrystalline intermetallics with room temperature deformability enabled by nanometer thick grain boundaries

Abstract

Although intermetallics are attractive for their high strength, many of them are often brittle at room temperature, thereby severely limiting their potential as structural materials. Here, we report on a previously unidentified deformable nanocrystalline CoAl intermetallics with Co-rich thick grain boundaries (GBs). In situ micropillar compression studies show that nanocrystalline CoAl with thick GBs exhibits ultrahigh yield strength, exceeding 4.5 gigapascals. Unexpectedly, nanocrystalline CoAl intermetallics also show prominent work hardening to a flow stress of 5.7 gigapascals up to 20% compressive strain. Transmission electron microscopy studies show that deformation induces abundant dislocations inside CoAl grains with thick GBs, which accommodate plastic deformation. Molecular dynamics simulations reveal that the Co-rich thick GBs play a vital role in promoting nucleation of dislocations at the Co/CoAl interfaces, thereby enhancing the plasticity of the intermetallics. This study provides a perspective to promoting the plasticity of intermetallics via the introduction of thick GBs.

Additive manufacturing of an ultrastrong, deformable Al alloy with nanoscale intermetallics

“…The inverse pole figure (IPF) map in Fig. 3b acquired from high-resolution ASTAR orientation mapping by high-precision electron diffraction recognition 33 , 34 demonstrates the crystallographic orientation of Al and Al 3 Ti. The polycrystalline composite has colonies with dimension of ~ 1 μm.…”

Achieving room temperature plasticity in brittle ceramics through elevated temperature preloading

“…The intersection of slip bands has several consequences. First, slip bands due to the formation of high-density dislocations or SFs form barriers for the transmission of dislocations on inclined slip systems (57)(58)(59)(60)(61)(62). Prior studies show that the SFs can intercept the transmission of dislocations and contribute to strengthening and prominent work hardening in metallic materials (57,59,60,(63)(64)(65)(66)(67)(68).…”

“…Prior studies show that the SFs can intercept the transmission of dislocations and contribute to strengthening and prominent work hardening in metallic materials (57,59,60,(63)(64)(65)(66)(67)(68). Second, the intersection of inclined SFs leads to immobile dislocations, such as Lomer dislocations, and these sessile dislocations increase the barrier for the migration of partials and consequently increase the work hardening rate (57,58,62,69). Apart from the strengthening effect, one of the key mechanisms for SF-induced plasticity is attributed to the defaulting process where dislocations can glide along SFs, leading to substantial plasticity (57).…”